This patent specification is in the field of methods and equipment for assisting medical professionals in assessing cardiovascular risk of patients and bone condition and fracture risk of patients. More particularly, this patent specification pertains to taking x-ray measurements with a dual energy bone densitometer for at least one of the two x-ray energy ranges that the densitometer can measure, and processing these measurements to detect and quantify aortic calcification, to use the results in estimating cardiovascular risk, and to report the outcome in particularly useful ways.
The abdominal aorta is a large, fluid filled vessel comprised of soft tissue. It can be barely visible on conventional x-ray images and is typically is visualized with the use of a radio-opaque contrast material. A vessel that is calcified usually presents with a linear or eggshell calcified pattern which is typical of calcification in the wall of a fluid filled structure. The history of using radiographs to identify abdominal aortic calcifications is well-established 1,2,5,11,14,15,16. (The superscript numerals refer to the documents cited at the end of the detailed description; all of those cited documents are hereby incorporated by reference in this patent specification.) A recent (2005) review article of methods for detection of abdominal aortic calcifications describes three primary methods: plain radiograph, ECT, and CT. It concludes, “Presently no modality has been accepted as the gold standard for the measurement of abdominal aortic calcification,” 5 but observes that “The simplest method of detecting abdominal aortic calcification is with plain abdominal X-ray.” 5 
Abdominal Aortic Calcification (AAC) is seen anterior to the lumbar spine in lateral view and is graded in severity by several methods8-10 related to the length of the AAC seen in the image. The published literature indicates a graded association between the length of the AAC seen in the image and the risk of future morbidity and mortality.1,3,6,7 In a typical grading scheme, the posterior and anterior walls of the aorta are graded in the area in front of the L1-L4 vertebra for total length of calcifications seen. For example, 0,≦1 cm, 1 to 2.4 cm, 2.5 to 4.9 cm,≧5 cm is considered, absent, dubious, mild, moderate, and severe, respectively.10 It has been reported that AAC is diagnostic for arteriosclerosis1-4. AAC is believed to be strongly associated with a number of diseases, independent of traditional clinical risk factors such as age, cigarette use, diabetes mellitus, systolic blood pressure, left ventricular hypertrophy, body mass index, cholesterol, and HDL cholesterol.1,3,5-7 The known literature identifies plain radiography, CT and ECT as the modalities to be used for AAC detection and quantification. MRI is also referenced as a modality in connection with assessing atherosclerosis.23 
A different modality, dual x-ray energy bone densitometry, has long been used for other purposes, mainly to obtain bone condition assessment information, including the projected bone mineral density (BMD, in g/cm2) at various anatomical sites, using dual energy x-ray absorptiometry (DXA) techniques that do not involve CT scanning such as in qCT (quantitative CT). One example of DXA systems is available from Hologic, Inc. of Bedford Mass. under the trade name Discovery. It has an examination table and a C-Arm at opposite ends of which are mounted an x-ray tube and a multi-detector array. The patient is positioned on the examination table between the x-ray tube and the detector array of the C-arm. For the assessment of bone mineral density, a fan-shaped beam of x-rays from the tube and the detector are scanned as a unit axially along the patient, while the x-rays are alternatively pulsed at high and low energy ranges. By comparing the relative attenuation of the x-rays at the two energies, the contributions to the attenuation due to the soft tissue can be subtracted. In other equipment, dual energy x-ray measurements are obtained by using a steady x-ray beam of relatively broad energy range impinging on two sets of detectors that measure respective energy ranges of the beam. At least in principle, similar results may be obtained without scanning, using an x-ray beam of a sufficient cross-section and a 2D array of detector elements. In each case, an image can be obtained of the bony structure of the body by the soft-tissue subtraction method. This image is then input into BMD analysis, which calculates and reports the BMD. The image can be displayed by showing it on a screen and/or printing it and can be stores in PACS or other storage/retrieval systems together with other densitometry and patient data.
When the patient's spine is scanned with a dual energy densitometer, the displayed image is similar to that in conventional spine radiography except that it requires many times less x-ray exposure and the entire spine or any desired part thereof can be scanned in one pass and shown as a single image. The image can be derived from measurements at both x-ray energy ranges or at one of them (single energy image). In the case of systems such as the Discovery, a single energy image can be obtained by selecting a fixed, relatively narrow energy range rather than alternating between two energy ranges. If a dual energy image is already available but a single energy image is desirable for some reason, it can be extracted simply by using only the x-ray detector outputs for one of the energies. In systems that use two sets of x-ray detectors, a single energy image can be extracted by using only the output of only one of the detector sets.
One of the options for densitometers offered by Hologic, Inc. is available under the trade name Instant Vertebral Assessment (IVA), sometimes referred to as vertebral fracture assessment (VFA), wherein vertebral deformities can be evaluated either quantitatively or visually, similar to standard quantitative and visual conventional radiograph or CT reading methods. IVA images are lateral spine images typically taken at single energy. While the images produced using x-ray bone densitometry IVA are not of sufficient quality for general radiological use, it has been observed that the quality of IVA images is similar to that of abdominal radiographs for visualizing abdominal aorta calcifications. In fact, AAC can be seen in DXA images sufficiently well to have allowed the Food and Drug Administration (FDA) to clear (510K clearance K060111 approval Apr. 24, 2006) Hologic Inc. for visualizing AAC with its DXA equipment.